1. Field of the Invention
This invention relates to automated handling of an integrated circuit during test of that integrated circuit and, more particularly, to an apparatus, kit and method used to adjust and/or maintain optimal deflection of an integrated circuit lead when contacting a test socket conductor.
2. Description of the Related Art
The sequence of steps used in forming an integrated circuit often culminates in an assembly or packaging operation. Assembly involves hermetically sealing the integrated circuit or die inside a carrier, or within an encapsulant injected about the die. A result of the assembly operation is to protect the integrated circuit against contaminants arising from the environment into which it is placed. Only leads extend from the packaged product into the environment. The leads are electrically connected to bond pads generally arranged around the periphery of the integrated circuit. Depending on the size or complexity of the integrated circuit, the leads can take on numerous configurations and/or arrangements, and therefore the packaged product can be classified as a dual-in-line package (DIP), a quad flat package (QFP), a ball-grid array (BGA), a single-level integrated module (SLIM), for example.
Before the packaged product can be used on, for example, a printed circuit board (PCB), it is necessary that the circuit be tested after the assembly operation and before its use in the field. For example, placing the integrated circuit inside the carrier or injecting encapsulant about the circuit may damage or skew the operating parameters of the integrated circuit. As such, mechanisms have been employed to rapidly test packaged integrated circuit prior to shipping those circuits to a customer.
A common test mechanism involves placing a test head against the integrated circuit leads. The test head contains high speed circuits which generate test signals and measure the result of those signals upon the integrated circuit. Thus, a test head may employ multiple signal generators as well as multiple voltage and/or current meters. The test head may also include a test socket. The test socket is one that is unique to the integrated circuit being tested, often referred to as the "device under test" or DUT. A plurality of test conductors extend from the test socket in registry with leads extending from the packaged product or DUT. Depending on the arrangement of those leads, the test socket can be configured in numerous ways with associated test conductors arranged unique to those leads.
A handler is used to place the DUT such that its leads extend against the test socket conductors. Most modem day handlers use a pick-and-place technique, whereby DUTs are drawn in succession from an input position to a holding device. The holding device is then moved toward the test socket with the DUT securely fixed within the holding device. After contact between the leads and the test conductors have been accomplished, and the test signal stimuli sent and results recorded, the holding device and DUT are then drawn away from the test socket. Based on the outcome of the test relative to the integrated circuit specification, the pick-and-place mechanism within the handler thereafter places the DUT in the appropriate bin position.
A primary function of the handler is to repeat movement of the holding device and DUT in rapid succession from one position to another. This entails repeatably placing leads of the DUT in accurate alignment with test conductors emanating from a test socket. At best, this is difficult to achieve. For example, many modem QFPs may have a hundred or more leads extending from a periphery less than three centimeters per side. Moreover, the pitch distance between leads may be less than 50 mils. Any misalignment between those leads and the test conductors may cause improper electrical contact or, in the worst case scenario, bending of the leads or test conductors. Even in instances where the DUT is leadless, or utilizes solder balls rather than leads, misalignment of those leadless receptors and the test conductors might prevent contact between the receptors and test conductors and/or damage the elongated test conductors which extend from the test socket. Misalignment may cause the test results to indicate an open circuit or failure when, in fact, the DUT is not a failure. The stimulus applied by a misaligned test conductor may contact a neighboring lead and damage circuits connected to that lead.
Conventional mechanisms for aligning leads to test conductors primarily focus upon the test head and the handler. That is, many alignment mechanisms rely on the distance between the test socket and a test head coupler upon the test head remaining fixed over time. There is generally another coupler upon the handler arranged a pre-defined distance from the point at which the DUT is delivered from the handler toward the test head. That distance is supposed to be the same distance as that which separate the test socket and the test head coupler. In this manner, the coupler upon the test head and the coupler upon the handler connect with one another and, hopefully, the test socket will align with the DUT. However, after inserting multiple DUTs in succession against the test socket, the delivery mechanism used by the handler will begin to wear. The extent of that wear will degrade or skew the delivery point from its initial delivery position. This may result in misalignment of the DUT leads relative to the test conductors. It would therefore be beneficial to derive an alignment mechanism which can maintain the alignment after repeated use, and can also expeditiously establish alignment of the first DUT to the test socket at the moment after which the test head and handler is retrofitted with a test kit. Thus, the desired alignment mechanism would prove advantageous if it can be obtained as a kit, comprising the test socket and the DUT holding mechanism. That kit would be particularly useful if it contains a mechanism not only to ensure transverse alignment of the leads to the test conductors, but also maintains a proper depth by which a respective lead is thrust upon a corresponding test conductor. Maintaining alignment in three dimension for dissimilar lead arrangements of numerously different packaged products would serve to minimize damage to the DUT, damage to the test socket, and waste of what would otherwise be electrically acceptable DUTs.